1. Field of the Invention
The present invention relates to a heart monitoring device, AS WELL AS to a system including such a device and to a manner of using the system. The device is of the type used to monitor the performance of a heart of a human or animal being. The device may also be able to deliver electrical stimulation pulses to the heart.
2. Description of the Prior Art
Several different devices for monitoring the performance of a heart are known. Often these devices also are able to deliver stimulation pulses to the heart. Such heart stimulation devices, or pacers, are normally arranged to stimulate the right ventricle of the heart. It is also known to stimulate the left ventricle. In particular for the treatment of congestive heart failure (CHF) or other severe cardiac failures, it is known to stimulate the left ventricle, or both ventricles, in order to optimize the hemodynamic performance of the heart. Some of these monitoring or stimulation devices are arranged to sense an impedance between electrode surfaces that are positioned in or at the heart and which are connected to the device. The sensed impedance may be used to control different pacing parameters.
U.S. Pat. No. 4,733,667 describes a cardiac stimulator apparatus arranged with a lead that is preferably positioned in the right ventricle. The lead has a number of electrodes. The apparatus generates a signal corresponding to the impedance between two electrodes. The apparatus also includes a differentiator that produces a first derivative of this signal. The apparatus also has a peak detector that identifies the peak value of the first derivative on a beat-by-beat basis. The variation of this peak value is used to control the pacing rate. The pacing rate is thereby adapted to the level of exercise of the patient carrying the cardiac stimulator.
U.S. Pat. No. 5,720,768 describes different possible electrode positions in order to stimulate or sense the different chambers of the heart.
U.S. Pat. No. 5,154,171 describes the use of impedance values to control the pacing rate. The pacer described in this document is only arranged to stimulate the right side of the heart.
U.S. Pat. No. 6,070,100 teaches that electrodes may be positioned in both the left and the right atrium as well in the left and the right ventricle. The document describes the possibility of sensing the impedance between different electrodes. The sensed impedance values may be used to improve the cardiac output. The document mentions that a linear relationship exists between the peak dz/dt and the peak ejection rate.
Published U.S. application Ser. No. 2001/0012953 describes bi-ventricular pacing. An impedance may be measured between electrodes on the right and the left sides of the heart. The variation of the impedance with time is detected. The detected impedance variation may be used in order to synchronize the contraction of the ventricles.
Published U.S. application Ser. No. 2001/0021864 describes different manners of using the proximal and distal electrodes of different leads in order to inject a current and to measure an impedance. The measured impedance value may be used in order to maximize the cardiac flow.
It is often difficult to determine the specific cause of a heart problem. For example, for a patient suffering from congestive heart failure (CHF) it is often difficult to know what causes this problem. The cause may be a systolic dysfunction or a diastolic dysfunction. The systole relates to the contraction of the heart, i.e. the pumping phase. Diastole relates to the phase when the heart is relaxed, i.e. when the ventricles are being filled with blood.